Vitamin E or tocopherol is a fat-soluble vitamin functioning as an antioxidant, protecting the cell membrane. As with all vitamins, the body does not form vitamin E. It solely forms from photosynthetic processes of plants, and therefore must be consumed from outside sources in small quantities. It is found abundantly in olive and sunflower oils, as well as nuts, soybeans, avocados, wheat, and green leafy vegetables.[1]

Vitamin E encompasses eight forms, including alpha, beta, gamma, and delta-tocopherol and alpha, beta, gamma, and delta-tocotrienol. However, only alpha-tocopherol is found in abundance and maintained well in human plasma.[2][3] Vitamin E supplements usually contain all isomers of alpha-tocopherol and have about half the activity level of natural sources. While other forms of tocopherols exist, only the alpha form or equivalents are measured for standard dietary sufficiency.

As with all fat-soluble vitamins, transport and absorption require intact fat digestion mechanisms. Fat metabolism involves lipases, both lingual and gastric, bile salts, pancreatic enzymes, and intestinal absorption. Tocopheryl-ester bonds are broken down by pancreatic enzymes.[4] Chylomicrons then transport alpha-tocopherol through the lymphatics to the liver. Once broken down in the liver, tocopherol is released from the chylomicrons. Alpha-tocopherol transfer protein is selective for alpha-tocopherol over other vitamin E forms and helps to package the molecule with low-density lipoprotein, which is subsequently secreted into the bloodstream.[4]

Of the fat-soluble vitamins, deficiency of vitamin E is uncommon. Disorders leading to disruption of fat metabolism are the usual causes of deficiency.[5][6][7] Cystic fibrosis or chronic pancreatitis can lead to pancreatic enzyme insufficiency. Disorders such as primary biliary cholangitis, primary sclerosing cholangitis, or decompensated cirrhosis will lead to cholestasis. This condition, in turn, will lead to an insufficient amount of bile necessary for normal fat absorption. Long-standing, severe cholestasis will eventually lead to low levels of vitamin E.[6][7] Resection of the bowel or disease of the small intestine can also cause deficiency due to decreased absorption of vitamin E. Bile acids are absorbed in the terminal ileum, and therefore, Crohn disease or amyloid infiltration will decrease the pool of bile acids and hence decrease fat absorption.[6][7]

Ataxia with vitamin E deficiency or AVED is a genetic disease caused by a mutation in the alpha-tocopherol transport protein, TTPA.[8][9] AVED usually manifests in pre-teen to teenage years and clinically manifests with ataxia, dysarthria, decreased proprioception and vibratory sensation as well as decreased reflexes due to the neurologic dysfunction linked to vitamin E deficiency.  A mutation of microsomal triglyceride transfer protein will lead to abetalipoproteinemia. In this disorder, there are absent or very low levels of low-density lipoproteins, and consequently, low levels of vitamin E transport, as well as other fat-soluble vitamins.[10] Vitamin E deficiency can clinically manifest with neuromuscular disruption. Neuropathy has variable involvement of the peripheral nervous system causing gait disturbance, loss of proprioceptive, and vibratory sense.[8][11] Red blood cell lifespan is shortened in chronic vitamin E deficient patients, clinically presenting with hemolysis.[5]

The use of alpha-tocopherol as a preventative antioxidant has been studied concerning cardiovascular disease, cancer, age-related macular degeneration, nonalcoholic fatty liver disease, and Alzheimer disease. The theory is that lipid oxidation plays a pivotal role in the development of cardiovascular disease and that the use of antioxidants as adjunctive therapy is useful for prevention. However, studies of vitamin E in the prevention of cardiovascular disease have not proven beneficial, with inconsistent outcomes and inherent study limitations.[12][13]

Antioxidant use of vitamin E in the prevention of cancers has also not shown to be effective and may increase the risk of prostate cancer. In the SELECT trial, researchers studied selenium and vitamin E to see what role there was for supplementation to decrease the incidence of prostate cancer. Participants were randomly assigned to either supplementation with selenium, vitamin E, both or placebo. The study resulted in an increase in incidence in those in the vitamin E only group. Other trials on the role of vitamin E and prostate cancer showed conflicting results.[4][13][14]

The progression of nonalcoholic fatty liver disease has shown to be decreased by high dose supplementation of alpha-tocopherol.[15] Long term studies remain necessary to show continued benefits. With age-related macular degeneration, a combination of antioxidants as an adjunctive therapy has shown to slow progression but has not proven to prevent development. Additionally, high dose vitamin E correlates with an increased progression of retinitis pigmentosa.[16][17] Alpha-tocopherol high dose supplements may also play a role in slowing the progression of Alzheimer disease.[18]

The primary mechanism of action of alpha-tocopherol is as a scavenger of free radicals. Peroxidation of polyunsaturated fatty acids in the cell membrane from free radicals leads to damage. Vitamin E plays a protective role. It also functions to inhibit aggregation of platelets, monocyte adhesion, and proliferation of cells.[1][4]

Routine supplementation of vitamin E is not recommended for the non-deficient child or adult. If a deficiency is detected or a person suffers from a disorder leading to absent or low levels of vitamin E, oral supplementation is available over the counter. For children, treatment doses are usually 25 to 50 international units per kilogram per day. For adults, typical requirements vary from 75 to 800 international units per day. Intramuscular vitamin E is not readily available but may be necessary for severe cholestasis or those with genetic disorders, with injections occurring weekly.[16]

Common side effects of alpha-tocopherol supplementation include nausea, headache, changes in vision, gastrointestinal upset, risk of hemorrhagic stroke, mild increase in urine creatinine, and necrotizing enterocolitis. There is a potential risk of increased bleeding intraoperatively, as vitamin E is known to inhibit the aggregation of platelets. Yet it has not been shown in those who are not already on antiplatelet or anticoagulants.[19] Alpha-tocopherol undergoes metabolism in the liver CYP450 enzymes and therefore monitoring for drug interactions if the patient is on medications that inhibit or induce these enzymes is recommended.[4]

Vitamin E supplementation is contraindicated in persons with known allergies to the vitamin or components of the formulation.